Medical radiography makes use of photographic recording materials (called X-ray films below) having at least one radiation-sensitive silver halide emulsion layer on both sides of a carrier in combination with reinforcing sheets. The physical and photographic properties of X-ray films determine their suitability in terms of allowing the radiologist to make a reliable diagnosis of diseases.
In addition to the uniform high quality requirements made of today's X-ray films, fast availability of the images developed from them is a significant aspect of the value offered by X-ray films. Fast availability is critical in those instances where pictures which are taken during operations are needed to provide information on the further course of the surgery.
Moreover, in hospitals or large physicians' practices, it is often the case that pictures from several imaging devices such as, for example, X-ray machines, laser cameras, devices for monitor photography and copiers for X-ray films are processed in the same film processor. Therefore, there is a desire for the shortest possible processing times--less than 60 seconds--for X-ray films as well as for other photographic films in such hospitals and physicians' practices.
The processing time of a photographic film depends primarily on the composition of the film in question, on the structure and on the mode of operation of the particular film processor, as well as on the developer solution and the fixing bath used in the film processor. The dryer geometry, drying time of the film processor, and absorption of process water by the particular photographic film all influence the drying of the photographic films in the film processor and these properties are of special importance in this context.
The processing time is defined here as the time that an X-ray film in the standard format having edge lengths of 0.35.times.0.35 meters needs to pass through a film processor, starting when the X-ray film is pulled in and ending with the complete release of the developed X-ray picture. This period of time is also referred to as the "nose to drop" in the literature.
A photographic silver halide recording material is said to be fast-processing if it can be processed in a film processor within 30 to 60 seconds.
U.S. Pat. No. 4,897,340 describes an example of a roll processor as well as a formulation for a developer used in it as well as a fixing bath suitable for this processing.
In order to reduce the processing time of photographic films, EP-A 0,248,390 proposes the reduction of the total gelatin application to a range from 2.2 to 3.1 g/M.sup.2 per side. However, this has a detrimental effect on certain properties of X-ray films such as, for example, wet pressure marks, scratch-resistance, grain, printing desensitization as well as the picture quality of the image made with this material.
As another way to shorten the processing time of X-ray films, it has been suggested to reduce the swelling of the binder by means of greater cross-linking. This measure, however, has a detrimental effect on the photographic properties such as gradation, sensitivity and maximum density.
A simultaneous reduction of binder and silver halide application in the recording material leads to a lower maximum density and a greater print through and thus to worse image sharpness of the picture made with this material. This can only be unsatisfactorily compensated for by using filter dyes, since the filter dyes cannot be completely washed out in the envisioned short processing time and thus they have a negative impact on the picture coloration of the X-ray image made in this manner.
U.S. Pat. No. 4,797,353 proposes another way to quickly process X-ray films which consists of using polymers such as polyacrylamide and/or saccharose in the silver halide or protective layer. These polymers are washed out during the development process.
However, the washable polymers contaminate the processor liquids and are thus disadvantageous. Moreover, such films with a low weight ratio of non-washable binder to silver have poor wet pressure mark properties.
Until now, no photographic recording material has been found for medical radiology that can be processed within 60 seconds with a film roll processor, while also displaying very good physical and photographic properties as well as high picture quality.
The photographic recording materials which have been proposed so far for medical radiology and which can be processed within 60 seconds also yield differing sensitometric data as a function of the processing time. This is not desirable in actual practice since different imaging parameters are needed for different processing speeds.